"A group of researchers has fabricated a single-atom transistor by introducing one phosphorous atom into a silicon lattice. Through the use of a scanning tunnelling microscope and hydrogen-resist lithography, Martin Fuechsle et al. placed the phosphorous atom precisely between very thin silicon leads, allowing them to measure its electrical behavior. The results show clearly that we can read both the quantum transitions within the phosphorous atom and its transistor behavior. No smaller solid-state devices are possible, so systems of this type reveal the limit of Moore's law - the prediction about the miniaturization of technology - while pointing toward solid-state quantum computing devices."

Once the message is read, it is destroyed. And, with a low probability of natural failure, would mean that a single transmitted secure-mode packet would signal a security breach and a new secure protocol would be enacted.

Snooping would disrupt communications of secure data, but the information itself would be largely secure (save for the odd packet here or there...).

It's true, while quantum computing closes the door on conventional encryption, it opens another door for quantum encryption. But unfortunately quantum encryption is not a direct substitute for PKI, leaving us to revert to point to point security. Without a CA, quantum entangled material would need to be exchanged and managed between parties beforehand (think every devices*website, wholly unrealistic). Or the traffic would have to be routed through a trusted proxy which has a secure quantum encrypted channel to both parties and is responsible for securing the traffic between them (more likely, but less ideal).

Also, quantum encryption suffers from the same bootstrapping issues as conventional encryption. You may have gotten a secure "quantum encryption card" in the mail, but without an out of band mechanism to validate it's authenticity (traditionally PKI), it's vulnerable to man in the middle attacks.

User <-> Service // normal secure quantum tunnel

User <-> Attacker <-> Service // attacker impersonates user to service, and impersonates service to user by swapping the quantum atoms and proceeds to mount a conventional man in the middle attack.

To address this using quantum encryption, one would probably need a third party which is already secure to validate that the bits the user is transferring match those seen by the service. This test would need to be done at the beginning of every session. However all this introduces more complexity and new failure modes because there's no quantum equivalent to PKI's offline authentication.

I'm just learning about quantum encryption so let me know if there are any errors in my understanding.